1. Field
Embodiments are disclosed relating to energy storage cells, and in particular to a cap for an energy storage cell that provides a hermetic seal.
2. Description of the Related Art
Energy storage cells are ubiquitous in our society. While most people recognize an energy storage cell simply as a “battery,” other types of cells may be included. For example, recently, ultracapacitors have garnered much attention as a result of their favorable characteristics. In short, many types of energy storage cells are known and in use today.
As a general rule, an energy storage cell includes an energy storage media disposed within a housing (such as a canister). While a metallic canister can provide robust physical protection for the cell, such a canister is typically both electrically and thermally conductive and can react with the energy storage cell. Typically, such reactions increase in rate as ambient temperature increases.
The electrochemical or other properties of many canisters can cause poor initial performance and lead to premature degradation of the energy storage cell, especially at elevated temperatures.
Aluminum is attractive to designers of such housings, however, use of aluminum is fraught with complications. For example, no one has been able to provide a hermetic seal with an aluminum housing (i.e., a seal with a leak rate of less than 5 E-6 std cc He/sec). Known techniques for providing an hermetic seal involve use of glass-to-metal sealing techniques, which typically involve fusing glass to stainless steel. Generally, the temperature required to achieve this type of seal is in excess of 1,000 degrees Celsius, which is well beyond the melting point of aluminum (660 degrees Celsius).
What are needed are methods and apparatus for providing an aluminum housing for an energy storage cell. Preferably, the methods and apparatus result in improved performance at a minimal cost.